The present invention relates to an elastic compensation chamber, with variable volume, with a telescopic form, to dissipate energy hydraulically, and is especially intended for the suspensions of railway rolling stock.
For these suspensions, the most common damper mechanisms, of the telescopic type, have a working cylinder filled with liquid and divided into two chambers by a piston equipped with calibrated valves determining the hydraulic resistance and whose shaft linked to the moving mass is guided through one of the faces of the cylinder. An annular volume surrounds the working cylinder and communicates through a calibrated valve with the working chamber opposite the piston shaft. Within the working cylinder, the variation of the volume of the incompressible liquid, resulting from the alternating movements of the shaft bearing the piston engenders braking forces which transform mechanical energy into heat.
The principal disadvantages of these devices result from the simultaneous presence of oil and ambient air within the various working chambers, which, at rest or at excessively small amplitudes of movement, provokes loss of priming of the mechanism due to the low level of the oil, engendering the phenomenon of cavitation.
In order to avoid such disadvantages, especially in the case of very low amplitude movements, as well as in the case in which the dissipator is called upon to assume some nearly horizontal position, and in order to compensate for the variation in liquid volume resulting from alternating movements of the shaft, hydraulic dissipators are used in which the reserve liquid within the surrounding annular volume is maintained under pressure by apparatus using mechanical springs or using elastic envelopes filled with air or some other gas under slight pressure.
However, these devices in general form an insulating screen around the working cylinder, thus hindering a rapid removal of the arising heat. This results in a rapid wear of the moving parts and even seizure, as well as decomposition of the oil employed, destruction of the joint seals, and of the elastic envelope itself.
While prior devices of this character (as in French patent No. 2,238,606--U.S. Pat. No. 3,945,663--and French patent No. 1,313,606, for example) involve similar shock absorbers including a deformable gas chamber, in all cases, this chamber acts as a thermal shield since it prevents the natural oil flow between the hot cylinder and the external tube at least in one sense (radial or axial) due to the fact that either the chamber is in close contact with the cylinder and the tube, or the chamber substantially surrounds the cylinder. Such a thermal shield results in the above-described disadvantages.